Volume-rendered images are very useful for representing 3D datasets, particularly in the field of medical imaging. Volume-rendered images are typically 2D representations of a 3D dataset. There are currently many different techniques for generating a volume-rendered image. One such technique, ray-casting, includes projecting a number of rays through the 3D dataset. Data along each of the rays is sampled, and then mapped to a color and transparency. Next, the data is accumulated along each of the rays. According to one common technique, the accumulated data along each of the rays is displayed as a pixel in the volume-rendered image. In order to gain an additional sense of depth and perspective, volume-rendered images are oftentimes shaded based on a light direction. The shading helps a viewer to more-easily comprehend and visualize the true three-dimensional shape of the object represented in the volume-rendered image. According to conventional shading algorithms, shading may be used with volume-rendered images in order to convey the relative positioning of structures or surfaces in the volume-rendered image.
Some conventional systems allow the user to alter the light direction in order to more clearly illustrate one or more targeted features in the volume-rendered image. However, since the light direction may be selected from any angular positions in three dimensions and since the display is only two-dimensional, it is often difficult for a user to quickly understand the current light direction used for determining the shading of the volume-rendered image. Additionally, it may be difficult for a user to visualize exactly how a specific control input will adjust the light direction with respect to the volume-rendered image.
Therefore, for these and other reasons, an improved system and method for indicating light direction for volume-rendered images is desired.